Batteries may sustain internal damage and/or reduced performance if charged at a rate or voltage above a predefined upper limit. In many cases, over-voltage conditions may produce gaseous by-products and/or induce changes to the internal chemistry of the battery. Additionally, batteries generally have an internal resistance that varies inversely with temperature. When charged with a constant current, the voltage drop across the battery may vary proportionately with the temperature-dependant resistance. Therefore, at lower temperatures, a lower charging current must be supplied to ensure that the increased voltage drop does not exceed the battery's upper limit, as compared with a higher charging temperature.
In a hybrid vehicle context, a vehicle's traction battery may be charged using a power inverter module that operates using high speed switching transistors that may induce a voltage oscillation into the electrical charge. This voltage oscillation may be attenuated using capacitive filters, however, an increased amount of filtering comes at the expense of packaging space (i.e. more filtering requires larger capacitors that may be difficult to package within a vehicle engine compartment).